Sludge recovery apparatus and method

ABSTRACT

A paint spray booth sludge recovery system, apparatus and method is provided for water washed paint spray booths. The spray booths are used with a tank or pit which can accommodate flotation for removal of spent paint. Preferably, the tank has a drop box section, a chemical treatment section, a weir box section and a booth recirculation pump section. A series of weirs are used to separate the spent paint and send a concentration thereof from the weir box to a separator or centrifuge. The water level in the system is controlled by sensing the weir box water level to keep the water crests over the weirs at the desired levels. Scavenging and agitation are provided in the tank to keep it entirely clean for prolonged periods without any accumulation, even during downtime.

DISCLOSURE

This invention relates to paint spray booths and paint or sludgerecovery systems and method for such booth, and more particularly, towater washed booths that utilize one or more weirs and a solidsseparator.

BACKGROUND OF THE INVENTION

Heretofore, water washed paint spray booths have utilized sludgerecovery systems to separate the spent paint material picked up by thewater as it passed through the booth. In one type system, the watercarrying the spent paint is allowed to drop or flow out of the boothinto a recovery tank or pit. In the tank or pit, the water is treatedwith chemicals, such as flotation chemicals which assists the spentpaint material to separate or segregate, and, in this instance, float tothe top. After sufficient time for the separating or flotation action tooccur, the spent paint material floats to the top and is allowed to flowover a weir into a separation area wherein it can be concentrated. Fromthere, the concentration spent paint material is drawn off to acentrifuge which separates the spent paint from the remaining water, andthe remaining water is sent back and is reused in booth.

During the operation of the booth, and even during downtime, water inthe booth system tends to be reduced in quantity, either due toevaporation, water being blown out the booth eliminator section (thebooth having a motor driven fan to usually exhaust air, including somewater out of the booth) and just variations in operating conditions. Thelatter could be due to a single pit or tank serving more than one boothand one or more booths operating conditions being changed or shut down.Changes in both water quantity and consequently the water level and thesludge recovery can have adverse consequences, particularly on theoperations of sludge systems using weirs. For example, changes of waterlevel effects the water crests flowing over the weirs and theiroperation. Too large a water crest can cause excess water to be suppliedto the separator making it more difficult to extract the sludgeefficiently. Too little water in the crests, on the other hand, cancause hang ups of the sludge, and partial or complete blockages, andalso reduces the efficiency of the operation. Keeping a constant waterlevel in the tank is important as it helps keep weirs operatingconsistently. Heretofore, one attempt to do so was to try to use a floatcontrolling the make up water valve in the large pit in which thechemical action or flotation action takes place. While this systemworked, it was slow to react to changes and allowed considerablevariation in water level in other portions of the system. Due to thedifficulty in controlling the water level in such way, it was difficultto get consistent efficient operation of a system based on paint sludgeflotation and some times other systems were used such as sinking orsuspension, that is, causing the spent paint to first sink, be drawn offthe bottom or to be kept in suspension and just drawn off. Prior to thepresent invention, there was not a reliable way to maintain water levelefficiently and permit the use of spent paint flotation and weirs.

SUMMARY OF THE INVENTION

The present invention provides structure or means and a method to bettermaintain the water level in a paint spray booth sludge recovery systemto make the use of flotation and weirs highly efficient.

In the improved system, the water level is not measured in the largetank or pit of the chemicals section, but is instead measureddownstream, preferably, in a weir box having an entrance weir into whichthe water flows after the spent paint is treated and concentrated and/orseparated by flowing over this entrance weir. The invention providesexcellent control of the water level in the tank and a rapid response toa change in water may provide make up water. In the present invention,water and dispersed spent paint is taken out from the weir box to flowto the solids separation device, in this instance, a centrifuge wherethe sludge is essentially separated from the water. The sludge-freewater is first passed through screens and sent back to the booth pumpsthat provide the water circulation (recirculation) for the booth forreuse.

Another improvement is the provision of an agitation system within theweir box to keep the water and any spent paint material agitated so thatthe spent paint does not settle out. This agitation water flow from theweir box may be provided by a pump that returns water to the weir box tokeep it agitated.

Another improvement is the provision of a sludge withdrawal system whichmay utilize a separate pump to pick up water and sludge at the bottom ofa drop tank into which the booth first discharges the water and spentpaint, before the first weir. The material from the sludge withdrawalsystem is then discharged into a basket or screened area in the pit ortank to trap large sized spent paint material or sludge, but let thewater escape. If desired, the drop tank too may be provided with meansfor agitating the spent paint and water therein.

Additionally, a maintenance cycle may be provided with means forwithdrawing water and solids from any desired portion of the booth ortank and returning cleaned water to the system. Preferably, this actionoccurs in the tank before the first weir or drop section to keep itclean.

The entire operation of the booth tank and sludge removal system may beautomatically controlled either by a central processor or a PLC(Programmable Logic Controller).

OBJECTS OF THE PRESENT INVENTION

It is an object of the present invention to provide a spray booth sludgerecovery system which is maintenance free and keeps not only the boothbut also sludge system, itself, clean.

Another object of the present invention is to closely control the waterquantity in the booth sludge recovery system.

Still another object of the present invention is to closely monitor thewater level in the sludge recovery system so that a flotation spentpaint recovery system works well.

A further advantage of the present invention is to closely monitor thewater level to maintain consistent water crests over a weir.

Yet a further object of the present invention is to maintain consistentflowage over the sludge collection weir.

Yet another further object of the present invention is in providingagitation in the weir box and/or elsewhere in the system to increasecentrifuge efficiency and keep the weir box and/or other portions of thesystem clean.

Still a further object is to provide scavenging early in the sludgerecovery system to remove large clumps, particularly before reaching thechemicals treatment section of the booth.

Still yet a further object is to provide a means for a maintenance cyclewhereby the booth, tank and/or sludge removal system is cleaned duringdowntime.

These and other objects of the present invention will become apparentfrom the following written description and the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of the present invention showing aplurality of paint spray booths serviced by a single sludge recovery pitor tank.

FIG. 2 is an enlarged schematic plan view of the tank shown in FIG. 1.

FIG. 3 is a schematic elevational view of the tank shown in FIG. 2.

FIG. 4 is an enlarged schematic perspective view of the adjustable,flotation concentration baffles shown in the tank of FIG. 2.

FIG. 5 is an enlarged schematic perspective view of the weir box of thetank of FIG. 2.

FIG. 6 is a schematic similar to FIG. 5, but showing some alternativemeans for withdrawing fluid and a preferred float location.

FIG. 7 is an enlarged schematic plan view of the tank of FIG. 2, showingthe pipe and other system components and connections.

FIG. 8 is an elevational view of the tank of FIGS. 2 and 6 showing waterlevels at various times.

FIG. 9 is an elevational view of the upstream drop box into which thebooths first discharge the spent paint and water into the tank.

FIG. 10 is a view somewhat similar to FIG. 5 or 6 but showing how thewater and floating spent paint are concentrated as they flow past thebaffles, over the weir, and into the weir box.

FIG. 11 is a view similar to FIG. 7, but showing additional means foragitating the drop box.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a plurality, in this instance, four water washedspray paint booths 10, 12, 14 and 16 are shown. As is conventional,water is used in the booths to collect spent paint and to wash the airbeing discharged by the booths. The booths are generally provided with amotor driven exhaust fan and eliminating means to move the air throughthe booth, collect the paint and remove it from the exhausted air. Eachbooth discharges its wash water and spent paint from a discharge opening18, 20, 22 and 24 into first branch troughs or pipes 26, 28, 30 and 32,and a common trough on pipe 34. The trough on pipe 34 has a dischargeend 36. From end 36 the spent paint and water flows into a sludgeremoval or treatment pit or tank 40. The tank 40 could be from 5 to 15feet wide and 20 to 100 feet long and 4 to 10 feet high. For example, atank 40 could be 5 feet wide, 24 feet long and 6 feet high. The tank orpit has a top rim with four parts 42, 44, 46 and 48; there are alsosidewalls 50, 52, 54 and 56, and a bottom wall 60 to confine the waterand spent paint in the tank 40 for treatment.

The tank 40 preferably has several sections. These sections will bebriefly described here and in more detail later. The first section willbe called the drop box section 70. It is into this section that the washwater and spent paint from the booths first drops or flow. A verticaldrop of several feet or more is desired for the agitation airentrainment, and to help break up of larger sludge pieces or matter.Separating the drop box from the other downstream portions or sectionsof the tank, is a first baffle, preferably in the form of a first weir74 although water flows over the first weir. Downstream of the firstweir 74 is the chemical treatment section 78 wherein the chemicallytreated water is caused to interact with the spent paint. From thechemical treatment section 78, some of the water at the top surface ofthe tank, now due to the treatment carrying most of the spent paint,flows over a second baffle or weir 82 into a weir box portion or section90. The remainder of the water flowing from the chemical section 78,which is generally much freer of spent paint flows down below the weirbox 90, over a third baffle or weir 94, through a screens 96 to be drawninto the main supply pump 100 or pumps for the booth or booths (10, 12,14 and 16) to be recirculated by the pump for reuse to maintain thewater wash in the booths. The portion of the water and spent paint thathas gone into the weir box 90, will be, as is subsequently discussed,further cleaned and treated by a centrifuge (see FIG. 7) to separate outalmost all, over 99% of the spent paint.

Referring now to FIGS. 2 and 3, much of the steps and structure justdescribed can be seen in more detail. Further additional structure isshown in these figures and will now be described along with theirfunction and operation. The depth of the tank is shown as represented bythe arrow 110 and could be from 36 to 120 inches with about 60-96 inchesbeing preferred. The maximum water level that might be held in the tank,such as during downtime is represented by the broken line 114. Thearrows 118 and 120 indicate the distance that the maximum water level isbelow the tank walls, which might be 12 inches. As noted above, inaddition to the first and second weirs 74 and 82, the third weir 94 maybe provided between the downstream side of the weir box and the pumpwell portion or section 122.

In operation, water and spent paint flow from the discharge 36 into thedrop tank section 70, and all water and spent paint must flow over thetop edge of the first weir 74 into the treatment section 78.

The length of the chemical treatment section 78 is made long enough sothat, depending on the chemicals and paint used, they have sufficienttime to react to provide the desired action to the spent paint. Thiscould be a time period as quick as a few seconds or minutes, with thelatter being preferred to ensure full treatment. In the preferredinstance, the chemicals cause the spent paint to float. Other typepaints and chemicals could be used, such as those causing sinking orsuspension, but such would require changes in the scavenging structureand operation to accommodate such different systems. The flow of waterfrom the drop tank 70 over the first weir 74 causes a crest to form andflow over the weir as indicated at 124. As can be seen, the water level,when operating, in the chemical treatment section is below the waterlevel 125 of the drop tank section, as indicated by the dotted line 128.As is indicated by the dotted line 74′, the baffle 74 may be adjusted inheight to help control or provide a desired height or depth of waterbehind the baffle 74 (or 74′) as is desired or needed to form thedesired height water crest over weir 74. The adjustment can beaccomplished in various manners.

As is better shown in FIGS. 2, 3, 4 and 5, some of the water dischargedfrom the chemical treatment section 70 flows over the second weir 82,but before doing so, the floating spent paint material is concentratedtoward the center (plan view) of the tank's top surface by a pair ofconcentration baffles 130 and 132. The baffles, preferably, have asomewhat triangular shape (top view) and tend to cause or concentratethe spent paint material toward the center of the tank (in a plan view).Like the first weir 74, the concentrating baffles 130 and 132 areadjustable and can be moved in toward and/or out from the center of thetank as needed or desired to best handle and concentrate the spent paintmaterials flowing into the weir box 90. To accomplish this, the baffles130 and 132 are adjustably mounted as by mounting blocks 134 and 136 tothe second weir 82, or alternatively a cross member adjacent to thesecond weir 82 and extending across the tank, with fasteners (notshown). Of course, the baffles 130 and 132 could be secured by othermeans or structure.

As can be seen in FIGS. 2, 3 and 5, the weir box 90 comprises the secondbaffle 82, forming its upstream wall, a downstream higher wall 140 overwhich no flow occurs. The sides of the weir box 90 are formed by thesidewalls of the tank. The bottom of the weir box is closed off by afalse bottom formed by inclined walls 142, 144, 146, 148 and center flat(horizontal) wall 150. As can be better seen in FIG. 3, cleaner watercan flow from section 78 under the weir box 90 into the downstreamportion of the tank 40 and downstream of the weir box 90, while thefloated spent paint flows over the second weir 82 into the weir box 90.

From the interior of the weir box 90, the spent paint which has alreadybeen concentrated by the baffles 130 and 132 is withdrawn or sent to asolids separator in the form of a centrifuge 154 (see FIG. 7), toseparate the spent paint material as will be described later. As isdepicted in FIG. 3, the cleaner water flows over a third baffle or weir94 into the pump section 122 of the tank, then passing through screens96 which protect the pump 100, then into the pump 100 from, where forthe most part, it is sent to and reused in the booths.

Referring to FIG. 3, it can be seen when flotation is used, there arethree weirs 74, 82 and 94 and crests or the water flow over these weirsare important to proper and efficient operation. If the weirs haveinsufficient water flow over, i.e., insufficient crest, particularly forweirs 74 and 82, there is a tendency for the spent paint to collect orhang up, interfering with proper separation and operation. If the waterflow is too high and the crests too large, excess water is provided andthe centrifugal separation becomes more difficult and inefficient.

Heretofore, attempts have been made to control the level of the water inthe tank or pit 40, generally with a float controlling a valvedischarging make up water into the large chemical treatment section 78.As the volume and surface area of this portion of the tank are large,there has to be very significant or large change in the quantity ofwater before the float sensed it and could react to control it. In theprior art, when the float sensed a water drop, it caused its associatedvalve to open and added make up water to the tank. Consequently, therewere large variations in the water level.

In the present invention, the water level in the weir box is controlledand this is done using the float 160. When the float 160 senses a waterdrop (as indicated at 160′), it causes its associated valve 168 (FIG. 5)to open and adds make up water to the weir box 90. It could also be setup to admit water elsewhere into the tank or booth(s).

In FIG. 5, the float 160 controlling the make up valve 168 is shown atone side of the weir box 90. In FIG. 6, the preferred arrangement isshown, with the float 160′ centrally located. Further as a back up, justin case the float 160 or 160′ in the weir box 90 should become stuck,inoperative or fail, say as due to an accumulation of sludge or spentpaint, a back up float 170 operating in parallel to the float 160 or160′ to control the valve 168.

Preferably, the float 160, 160′ or 170 operates as an electrical switchand the valve 168 is an electrically operated solenoid valve to controlthe flow of make up water. The float may be a “Mini float” sold byAnchor Scientific, Inc., while the solenoid valve may be like that soldby Osco under Model No. 8210B56. As is shown in FIG. 5, a similararrangement could be provided for float 160′ or 170′. When the float 160drops, a switch inside the float closes (as is conventional) to providepower to open up the solenoid valve 168 to permit make up water to flowfrom the pipe 171 to pipe 173 and then into the tank 40, and preferablythe weir box section 90 thereof Of course, the make up flow could beelsewhere into the booth(s) or tank. The back up float 170 is providedin the pump section 12 of the tank 70. Preferably, the back up float 170may be located before/after the screens 96.

Due to the small volume of the weir box 90, compared to the overallvolumes of water in the booths and tank 70, or even any of the othervarious sections of the tank, the float 160 or 160′ in the weir box 90reacts very quickly to water level changes, and this keeps the waterlevel much more constant and, consequently, the desired crests over theweirs.

The tank 70 is sized according to the booth or booths recirculationrate. Generally, the length of the tank should be several times longerthan its width to provide for efficient chemical operation. A goodlength to width ratio is 5:1 so that there will be at least severalminutes time for the chemicals to react with the spent paint. Of course,this will vary with both paint and the chemical treatment. The size ofthe separator or centrifuge 154 used also is a factor. Generally, thewater volume, in gallons, in the weir box should be from 1-½ to somewhatover three times the gallons per minute (gpm) flow rate for theseparator or centrifuge. For example, a centrifuge with a flow rate of20, 40 or 60 gpm might have a weir box with a water volume of 33-66,66-100 or 100-133 gallons. For example, a system with a 40 gpmcentrifuge may have a weir box of about 80 gallons.

In addition to help keep the drop box 70 clean, a scavenging header 180is provided therein. The header itself is a pipe with a plurality ofopenings (say 1 inch diameter, 5 inches a part) along its lengththerein, permitting water to be drawn off via a pipe 182, through acontrol or butterfly valve 184, to a sludge or trash type or diaphragmpump 186 which is resistant to fouling. From the diaphragm pump 186, thematerial sucked into the header 180, such as large agglomerating ofpaint sludge which settles or falls to the bottom of the drop box 70, isdischarged through a flexible connector or hose 188, into a basket orstrainer 190 located above or in the chemical portion 78 of the tank.The large particles of spent paint is trapped in the basket 190, whichmay be periodically dumped, and the water flows back into the tank 70for use.

Additionally in the weir box 90, some of the water and spent paint isdrawn off the bottom of the box through a discharge 200 by a pump 202,the discharge 200 and pump 202 inlet being connected by piping 204 and avalve 210. From the pump 202, which is shown in the box 212 in FIG. 1,most of the spent paint and water is delivered (via pipes 201, 203, 205and 207) to the centrifuge or separator 154. In the separator, the spentpaint is separated, and the clarified water returned via pipes 230 and236 to the tank 40 and drop box section 70. A test outlet 209 closed offselectively by valves to obtain water from the tank or separator isprovided.

Further, some of the discharge from the pump 202 can be diverted foragitating the interior of the weir box 90. To this end, the pipe 240tees into pipe 203 and connects diaphragm valves 244 and 248 to somebutterfly nozzles 252 and 254. By controlling the various valves in thesystem, and particularly diaphragm valve 244, the rate of flow to thenozzles 252 and 254 agitation in the weir box 90 can be regulated to adesired level. The agitation insures the weir box 90 stays clean withoutany accumulation and keeps the spent paint there in a suspension to givea more uniform infeed to the centrifuge 220.

When the booth(s) is/are shut down, a maintenance cycle is provided andoperated and it has a maintenance header (again, a pipe with a pluralityof similar openings therein as for header 180) 260 into which water andany spent paint or trash may be drawn by a pump 264. The maintenanceheader and pump 264's inlet are connected via pipes 268 and 270. Thepump 264 discharges to a pipe 276 which in turn tees into the pipe 205providing flow to the separator 154. Thus, with the pump 264 inoperation during a maintenance period, the drop box may be kept clean byfeeding the collected water and materials collected by the header 260 tothe separator 154.

Additionally, as shown in FIG. 11, a pipe 282 can be connected to thedischarge of the pump 264, and via control valve 288 connected to pipes292 and 296, which in turn connect to nozzles 300 and 302 in the dropbox 90 to provide additional agitation therein, if desired.

While the preferred method and apparatus of the present invention hasbeen described, it should be understood that alternative equivalentsteps and elements fall within the scope of the appended claims.

What is claimed is:
 1. A method for controlling the water level in apaint spray booth sludge recovery system having said paint spray boothdischarging spent paint and water into a sludge tank, the sludge tankhaving a chemical treatment section, a weir separating the chemicaltreatment section, a weir box downstream of the weir receiving flow fromthe weir, a separator withdrawing spent paint and water from the weirbox and returning the cleaned water to the spray booth sludge recoverysystem, and comprising the step of measuring the water level in the weirbox and adjusting the water level in the weir box to keep it essentiallyconstant and thus better control the water level over the weir, saidstep of adjusting including the step of controlling the amount of makeup water added to the system over a period of time and further includingagitating at least some of the water in the system to keep materialstherein in suspension, including the step of scavenging at leastportions of the system during downtime to prevent accumulation.
 2. Amethod for controlling the water level in a paint spray booth sludgerecovery system having said paint spray booth discharging spent paintand water into a sludge tank, the sludge tank having a chemicaltreatment section, a weir separating the chemical treatment section, aweir box downstream of the weir receiving flow from the weir, aseparator withdrawing spent paint and water from the weir box andreturning the cleaned water to the spray booth sludge recovery system,and comprising the step of measuring the water level in the weir box andadjusting the water level in the weir box to keep it essentiallyconstant and thus better control the water level over the weir, the stepof adjusting including the step of controlling the rate of make up waterbeing added to the system.
 3. A method as in claim 2, the step ofreturning the cleaned water from the separator to the chemical treatmentsection and reusing the chemicals therein to treat additional spentpaint material.
 4. The method of claim 2, wherein the step of measuringincludes the step of controlling the level with a float.
 5. A method asin claim 2, wherein the step of measuring includes one of mechanicallyand electrically measuring the water level.
 6. The method of claim 2,wherein the step of adjusting includes the step of controlling the rateof water entering the weir box.
 7. The method of claim 6, wherein thestep of measuring comprises using a float to control the level of waterin the weir box.
 8. The method of claim 2, including the step of sizingthe weir box at least several times smaller in volume than the volume ofwater held in the chemical treatment section of the sludge recoverysystem so that any change in water quantity in the system show upquickly as a change in the water level in the weir box.
 9. The method ofclaim 2, further including the step of scavenging the flow of waterbefore it flows into the chemical treatment section of the sludge tankto remove large clumps of spent paint material.
 10. The method of claim2, including the step of agitating the water upstream of the weir box.11. The method of claim 2, including the step of scavenging at leastportions of the tank during downtime to prevent accumulation.
 12. Themethod for controlling the water level in a paint spray booth sludgerecovery system having said paint spray booth discharging spent paintand water into a sludge tank, the sludge tank having a chemicaltreatment section, a weir separating the chemical treatment section, aweir box downstream of the weir receiving flow from the weir, aseparator withdrawing spent paint and water from the weir box andreturning the cleaned water to the spray booth sludge recovery system,and comprising the step of measuring the water level in the weir box andadjusting the water level in the weir box to keep it essentiallyconstant and thus better control the water level over the weir, whereinthe step of adjusting includes the step of controlling the water beingadded to the tank downstream of the weir box.
 13. A method as in claims12, the step of returning the cleaned water from the separator to thechemical treatment section and reusing the chemicals therein to treatadditional spent paint material.
 14. The method of claim 12, wherein thestep of measuring includes the step of controlling the level with afloat.
 15. A method as in claim 12, wherein the step of measuringincludes one of mechanically and electrically measuring the water level.16. The method of claim 12, wherein the step of adjusting includes thestep of controlling the rate of water entering the weir box.
 17. Themethod of claim 16, wherein the step of measuring comprises using afloat to control the level of water in the weir box.
 18. The method ofclaim 12, including the step of sizing the weir box at least severaltimes smaller in volume than the volume of water held in the chemicaltreatment section of the sludge recovery system so that any change inwater quantity in the system show up quickly as a change in the waterlevel in the weir box.
 19. The method of claim 12, further including thestep agitating the water in the weir box to keep materials therein insuspension.
 20. The method of claim 12, further including the step ofscavenging the flow of water before it flows into the chemical treatmentsection of the sludge tank to remove large clumps of spent paintmaterial.
 21. The method of claim 12, including the step of agitatingthe water upstream of the weir box.
 22. The method of claim 12,including the step of scavenging at least portions of the tank duringdowntime to prevent accumulation.
 23. The method for controlling thewater level in a paint spray booth sludge recovery system having saidpaint spray booth discharging spent paint and water into a sludge tank,the sludge tank having a chemical treatment section, a weir separatingthe chemical treatment section, a weir box downstream of the weirreceiving flow from the weir, a separator withdrawing spent paint andwater from the weir box and returning the cleaned water to the spraybooth sludge recovery system, and comprising the step of measuring thewater level in the weir box and adjusting the water level in the weirbox to keep it essentially constant and thus better control the waterlevel over the weir, further including the step of agitating the waterin the weir box to keep materials therein in suspension.
 24. A method asin claim 23, the step of returning the cleaned water from the separatorto the chemical treatment section and reusing the chemicals therein totreat additional spent paint material.
 25. The method of claim 23,wherein the step of measuring includes the step of controlling the levelwith a float.
 26. A method as in claim 23, wherein the step of measuringincludes one of mechanically and electronically measuring the waterlevel.
 27. The method of claim 23, wherein the step of adjustingincludes the step of controlling the rate of water entering the weirbox.
 28. The method of claim 27, wherein the step of measuring comprisesusing a float to control the level of water in the weir box.
 29. Themethod of claim 23, including the step of sizing the weir box at leastseveral times smaller in volume than the volume of water held in thechemical treatment section of the sludge recovery system so that anychange in water quantity in the system show up quickly as a change inthe water level in the weir box.
 30. The method of claim 23, furtherincluding the step of scavenging the flow of water before it flows inthe chemical treatment section of the sludge tank to remove large clumpsof spent paint material.
 31. The method of claim 23, including the stepof agitating the water upstream of the weir box.
 32. The method of claim23, including the step of scavenging at least portions of the tankduring downtime to prevent accumulation.